The invention relates to a powder coating assembly as defined in the preamble of claim 1.
For workpiece powder coating, the workpiece is guided through a powder coating compartment and coated with powder inside that compartment. Not all of the powder fed into the compartment through the applicator devices does deposit on the workpiece. A large part of the excess powder settles on the floor of the compartment.
In the case of conventional compartments this excess powder is sucked out of the compartment by means of a fan. However, when it is attempted to remove the excess powder from the compartment simply by subjecting the exhaust opening to the low pressure generated by the fan, the suction effect remains restricted to a relatively small area around the exhaust opening. On the other hand, the powder continues to accumulate on the remainder of the floor areas.
This disadvantage can be mitigated by provision of a baffle means such as specified in EP 0 384 236 B1. Such a baffle means reduces the settling of powder on the floor of the compartment.
Another way of reducing accumulations is disclosed in EP 0 200 681 B1. In that case the floor of the compartment has the configuration of a V-shaped trough the sidewalls of which are inclined in opposite directions, an exhaust port being disposed at the lowest location. Excess powder now may slide along the inclined sidewalls of the trough down into the exhaust port. With this structure, however, the floor of the compartment is not walkable as would be desirable for purposes of inspection and maintenance work.
With another known compartment (EP 0 727 258 B1) the floor of the compartment is formed by a walkable discharge belt. Any powder accumulated on the floor is conveyed by the discharge belt through the compartment and to an exhaust opening at the front end. In this manner powder can be removed also from those areas which are not located in the direct vicinity of the exhaust opening.
All the compartments described above provide for conveyance of the excess powder through an exhaust opening either to a powder recovering installation or directly to a filter unit if recovery is dispensed with.
A powder coating assembly 1 is known from U.S. Pat. No. 5,107,756. The flow of excess powder in that case can be directed either directly to the filter unit or to a recovery unit, by means of a switchover flap. In addition, a shutoff member is provided which selectively may block a supply channel to the recovery unit or simultaneously block this supply channel and a return channel of the recovery unit. This structure is complicated and expensive. The switchover and shutoff elements are located at positions which tend to get very contaminated in operation. Cleaning when colors are changed, therefore, is very time consuming and does not produce satisfactory results.
It is the object of the invention to provide a powder coating assembly of the kind defined initially which permits quick and simple switchover from operation with filters to operation with recovery of excess powder, and vice versa, widely avoiding any contamination while allowing rapid, easy and efficient cleaning.
The powder coating assembly according to the invention, provides separation of the mode which includes powder recovery and the mode which includes direct filtering of the excess powder through the filter. In this way contamination is widely avoided and cleaning expenditure minimized.